Anti-tipping roller follower

ABSTRACT

An anti-tipping feature for a roller follower is provided that is positioned at the socket end of a Type II roller follower. The anti-tipping feature is designed to fit around the plunger of a lash adjuster. The feature has legs that extend down around the plunger to provide stability for the roller follower. Tipping of the roller follower is controlled by the formed legs that extend down the plunger. The length of the legs and clearance determine the amount of roller follower tipping. The valve guide wall height can be shortened enough to still provide valve containment and reduce moving mass which comprises a key component to engine performance.

This invention relates to a roller follower for a Type II internalcombustion engine and more particularly to a roller follower devisedwith an anti-tipping feature placed at the socket end of the rocker arm.

BACKGROUND OF THE INVENTION

A key factor for roller follower design is mass at the valve end.Reducing the amount of moving mass can improve engine performance byusing more aggressive valve lift profiles, which in turn can improveengine power, raise limiting speed, and reduce hydrocarbon emissions. Itis common knowledge a Type II valve train roller follower is configuredto include a socket end to engage a lash adjuster, a valve pad end toengage a valve, and a bearing between the ends that contacts an overhead cam. When the roller follower is placed in the head on the lashadjuster and valve, before the cam shaft is installed, there is a degreeof freedom for the roller follower to tip side to side. The rollerfollower needs that side to side freedom for any misalignment that mayhave occurred when the bearing was installed into the roller follower.This misalignment allows the roller follower to still be functional andperform as designed. During engine operation if the bearing is notexactly parallel to the valve pad the roller follower, without any valvecontainment feature, can slide off the valve stem causing the cylinderto misfire and reducing engine performance. To keep the roller followerfrom sliding off the valve integral formed guide walls or an additionalpart is added to the roller follower at the valve pad end.

Another important function of the rocker arm valve guide walls is toprevent the roller follower from tipping over and falling into theengine head during the automated engine assembly process. Once the camshaft is put into place during the assembly process the roller followerwill be securely held on the lash adjuster and valve tip. To keep theroller follower from tipping the rocker arm valve guide walls need to begreater than about 3 mm in height. This provides enough valve stem toguide wall contact to limit how much the roller follower can tip and notfall off. By adding wall height to control tipping you also addadditional moving mass which is undesirable for engine performance.

Consequently, there exists a need for a roller follower that combinesusing guide walls less then 3 mm to reduce valve pad end mass and stillprovide enough stability to not tip during engine assembly.

SUMMARY OF THE INVENTION

The anti-tipping arrangement of the invention comprises providing legsof a suitable height at the socket end of a Type II roller follower.This anti-tipping feature of the invention is advantageously devisedwith legs that extend down around the lash adjuster plunger to providestability for the roller follower.

The stability providing feature of the invention has no significantimpact on, i.e., is not a detriment to, the mass at the valve end.Additional advantages of the invention will be apparent from thedetailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a valve train including anoverhead camshaft with cam lobes, lash adjuster, valve and rollerfollower.

FIG. 2 is a perspective disassembled bottom view of the clip and rollerfollower with roller.

FIG. 3 is a perspective more detailed bottom view of the roller followerper se, i.e., with roller omitted.

FIG. 4 is a perspective view of the assembled roller follower with clipin place.

FIG. 5 is another perspective view of the assembled roller follower withclip in place.

FIG. 6 is a fragmentary cross-sectional view through the top of the lashadjuster with the roller follower of the invention in place.

FIG. 7 is a perspective view of the pivot clip of the invention providedwith an outer socket clearance hole, a plunger body clearance hole andflat clip legs.

FIG. 8 is a fragmentary perspective view of the roller follower with theclip device of FIG. 7 in place.

FIG. 9 is a fragmentary perspective view of the roller follower with analternative anti-tipping device comprising a wire clip in position onthe roller follower.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the figures of the drawings, FIG. 1 refers to a Type IIValve Train design which includes overhead camshaft 16 provided with cam10 having a cam lobe 11, lash adjuster 12, valve 13 and roller follower14. The roller follower 14 is in contact with the camshaft cam lobe 11.As the lobe camshaft 16 and cam 11 rotate the cam lobe 11 displaces theroller follower 14. The roller follower 14 pivots, i.e., reciprocates onthe lash adjuster 12. The lash adjuster is devised to maintain zeroclearance between the cam, rocker arm and valve throughout the liftevent so that there is no separation between the valve contact portion22 of the rocker arm and valve 13 causing what is known as valve lossmotion resulting in poor engine performance. The roller follower 14translates the rotating camshaft motion into linear motion which opensand closes the valve 13.

As shown in FIG. 2 and FIG. 3, elements of the roller follower areillustrated. The roller follower 14 comprises a main body 18 with sidewalls 20 generally comprising U-shape cross-section, pivot socket 19which engages the lash adjuster 12 and valve contacting portion 22. Anopening 21 is provided in the side walls 20 to mount a shaft 26 whichpasses through the roller follower body and is preferably surrounded byt multiple needle bearings 27 (shown in FIG. 1) and roller 17. Roller 17is positioned between side walls 20 and pivot socket 19 and valvecontacting portion, valve pad 22. The valve contact portion is providedwith guide extensions 23 that are parallel to side walls 20. As shown inFIG. 2, roller follower 14 is illustrated in accompaniment but notengaged with the anti-tipping clip 15.

In FIGS. 4 and 5 the anti-tipping clip 15 shown separate in FIG. 2 andFIG. 7 is engaged on the assembled roller follower 14.

FIG. 6 illustrates a cross-section at the top of the lash adjuster 12which engages the pivot socket 19 of the roller follower.

In FIG. 7 the pivot clip 15 which contains socket clearance hole 24,plunger body clearance hole 26 and clip leg 25 is shown.

In the enlarged fragmentary view of FIG. 8, the clip 15 in position isillustrated in greater detail.

FIG. 9 illustrates an alternated clip 30 with wire form legs 31 and 32,secured to the roller follower body 18a. Reference numbers followed bythe lower case “a” in FIG. 9 identify elements that function similar tothe earlier mentioned elements bearing similar numbers.

To keep the roller follower 14 from sliding off the valve 13 integralformed guide walls 23 or an additional part is added to the rollerfollower contiguous to the valve pad 22 end. Another important functionof the rocker arm valve guide walls is to prevent the roller followerfrom tipping over and falling into the engine head during automatedengine assembly process, e.g., in order to keep the roller follower fromtipping the rocker arm valve guide walls need to be greater than about 3mm in height. This provides reasonable assurance that enough valve stemto guide wall contact is provided so that any occurring tipping of theroller follower will not result in a displacement of the rollerfollower. It is to be noted that adding wall height to control tippingalso results in additional moving mass which is undesirable for engineperformance. It is thus seen that a roller follower is provided thatuses minimum necessary guide walls of the order of less than 3 mm toreduce valve pad end mass and still provide enough stability to preventtipping during engine assembly. The anti-tipping feature of theinvention is advantageously devised with legs that extend down aroundthe lash adjuster plunger to provide stability for the roller follower.The stability providing anti-tipping adjunct of the invention does notintroduce a significant impact on, i.e., is not a detriment to, the massat the valve end of the roller follower.

Although the invention has been described in terms of a specificembodiment, one skilled in the art can vary or substitute other obviouselements or embodiments and these are meant to be included herein. Theinvention is only to be limited by the scope of the appended claims.

1. In a roller follower that pivots about a lash adjuster of internalcombustion engines comprising a one-piece, cold-formed, elongate metalbody having a generally U-shaped cross-section and having anintermediate portion, a first valve contact end portion, and a secondlash adjuster contact end portion, said intermediate portion having twosubstantially parallel side walls and a large elongate upper opening,said first end portion having a top wall and two side walls extendingdownwardly therefrom generally inverted U-shaped recess to receive anend of a valve stem, said second end lash adjuster contact portionhaving a second top wall and side walls extending downwardly there from,the improvement comprises an anti-tipping clip secured to the lashadjuster end and having a pair of legs extended around the lash adjustercontact so as to afford stability for the assembly.
 2. The rollerfollower of claim 1 wherein legs of the lash adjuster clip comprises aflat configuration.
 3. The roller follower of claim 1 wherein the lashadjuster clip comprises a wire leg configuration.